Three Oaks Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Three Oaks Observatory clear sky chart from 2005-11-05 to 2017-09-23.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.
Observation TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(no limit)Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
55%
15651
23%
47010
17%
15609
61%
15609
29%
29207

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 15thNight
37%
718
22%
2327
12%
716
51%
716
25%
1444
January16th to endNight
38%
768
24%
2412
15%
768
48%
768
26%
1493
February1st to 15thNight
42%
704
25%
2108
14%
700
53%
700
30%
1286
February16th to endNight
38%
631
27%
1893
14%
631
51%
631
30%
1161
March1st to 15thNight
45%
720
28%
2024
16%
720
55%
720
35%
1195
March16th to endNight
49%
768
25%
2112
15%
768
56%
768
36%
1252
April1st to 15thNight
53%
718
25%
1976
18%
718
58%
718
37%
1178
April16th to endNight
58%
544
30%
1717
23%
544
66%
544
39%
918
May1st to 15thNight
62%
539
25%
1619
19%
539
68%
539
37%
937
May16th to endNight
71%
561
22%
1682
18%
561
74%
561
33%
1031
June1st to 15thNight
72%
540
14%
1620
12%
540
72%
540
27%
1069
June16th to endNight
75%
540
15%
1620
15%
540
75%
540
24%
1102
July1st to 15thNight
75%
510
12%
1530
11%
510
75%
510
25%
1044
July16th to endNight
74%
564
11%
1595
11%
531
75%
531
25%
1072
August1st to 15thNight
71%
539
11%
1671
12%
536
71%
536
21%
1169
August16th to endNight
64%
606
14%
1943
15%
606
64%
606
18%
1405
September1st to 15thNight
63%
720
14%
1980
13%
720
63%
720
21%
1413
September16th to endNight
59%
689
19%
1903
16%
689
61%
689
25%
1299
October1st to 15thNight
63%
660
33%
1823
29%
660
67%
660
38%
1068
October16th to endNight
58%
704
32%
2112
29%
704
65%
704
39%
1182
November1st to 15thNight
56%
700
31%
2167
26%
700
65%
700
38%
1186
November16th to endNight
49%
720
28%
2340
21%
720
60%
720
35%
1284
December1st to 15thNight
46%
720
24%
2340
20%
720
53%
720
28%
1415
December16th to endNight
41%
768
23%
2496
19%
768
49%
768
23%
1604

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

Occurrence of each ForecastData
Points
Cloud CoverDay
10%5%25%5%35%5%6%8%41%
47883
Night
9%425%5%345%5%8%45%
47214
TransparencyDay
39%8%11%17%16%6%
47584
Night
35%7%12%17%17%9%
47017
SeeingDay
11%313%22%26%22%
5532
Night
11%420%32%26%4
15656

By Month

Percentage Cloud Cover SE (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
13%6%35%43445%7%42%
1611
16th to endDay
14%5%33314447%45%
1809
February1st to 15thDay
13%6%25%5%2344446%
1750
16th to endDay
14%6%24423445%49%
1580
March1st to 15thDay
9%5%1442345%7%50%
1935
16th to endDay
12%5%24434445%48%
2111
April1st to 15thDay
10%5%2443445%6%48%
1977
16th to endDay
8%314433447%53%
2246
May1st to 15thDay
8%314425%5%5%7%50%
2331
16th to endDay
7%4245%25%6%6%10%43%
2431
June1st to 15thDay
9%425%6%47%7%8%8%34%
2340
16th to endDay
6%5%35%6%47%7%8%10%32%
2340
July1st to 15thDay
7%5%37%8%46%8%8%11%28%
2340
16th to endDay
7%436%7%49%8%8%12%26%
2465
August1st to 15thDay
10%6%37%8%6%8%8%9%10%20%
2274
16th to endDay
13%6%36%7%5%8%7%8%8%26%
2246
September1st to 15thDay
10%5%37%7%5%5%6%8%9%29%
1980
16th to endDay
13%6%26%6%45%45%7%37%
1894
October1st to 15thDay
11%5%24423446%52%
1807
16th to endDay
7%424323345%57%
1760
November1st to 15thDay
6%414413347%56%
1688
16th to endDay
12%414313445%53%
1620
December1st to 15thDay
14%6%34424447%44%
1620
16th to endDay
18%7%345%3345%6%37%
1728
January1st to 15thNight
12%6%345%345%46%44%
2327
16th to endNight
15%5%2442435%5%46%
2412
February1st to 15thNight
12%5%24324345%49%
2103
16th to endNight
11%5%25%423446%49%
1893
March1st to 15thNight
9%3145%24348%52%
2024
16th to endNight
9%314323445%55%
2112
April1st to 15thNight
9%32442445%6%51%
1976
16th to endNight
5%3233245%7%7%55%
1717
May1st to 15thNight
7%3134145%5%9%52%
1619
16th to endNight
44145%36%5%6%7%49%
1682
June1st to 15thNight
7%326%6%46%7%8%13%34%
1620
16th to endNight
6%325%6%48%7%7%11%35%
1620
July1st to 15thNight
6%5%346%45%7%9%13%33%
1620
16th to endNight
5%326%7%38%7%9%11%33%
1703
August1st to 15thNight
6%5%36%7%46%7%8%14%30%
1682
16th to endNight
9%5%47%6%45%6%8%11%31%
1943
September1st to 15thNight
9%6%36%7%45%6%6%9%33%
1980
16th to endNight
9%7%26%5%446%6%9%37%
1903
October1st to 15thNight
8%424313347%55%
1823
16th to endNight
8%414323345%57%
2112
November1st to 15thNight
8%314323446%56%
2167
16th to endNight
10%324323247%54%
2340
December1st to 15thNight
11%5%34423447%46%
2340
16th to endNight
13%7%35%5%2345%6%42%
2496

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
40%6%8%16%18%10%
1612
16th to endDay
38%46%17%22%10%
1809
February1st to 15thDay
40%46%14%22%12%
1752
16th to endDay
37%46%15%24%11%
1580
March1st to 15thDay
32%5%8%20%23%10%
1935
16th to endDay
36%5%10%17%21%8%
2112
April1st to 15thDay
35%5%8%19%22%8%
1977
16th to endDay
30%5%10%22%22%8%
2246
May1st to 15thDay
31%6%11%21%21%8%
2331
16th to endDay
34%8%15%22%14%3
2435
June1st to 15thDay
41%12%15%20%9%
2340
16th to endDay
40%11%16%19%9%1
2340
July1st to 15thDay
44%14%20%15%5%
2201
16th to endDay
44%15%19%15%4
2310
August1st to 15thDay
52%14%16%12%3
2261
16th to endDay
50%14%14%13%5%1
2246
September1st to 15thDay
46%12%13%13%11%2
1980
16th to endDay
45%6%12%14%16%4
1894
October1st to 15thDay
32%410%18%22%12%
1807
16th to endDay
29%46%16%28%15%
1760
November1st to 15thDay
27%38%18%25%15%
1688
16th to endDay
32%47%15%24%14%
1620
December1st to 15thDay
40%5%8%17%19%8%
1620
16th to endDay
47%49%17%13%8%
1728
January1st to 15thNight
39%5%8%13%20%11%
2327
16th to endNight
38%5%6%13%23%11%
2412
February1st to 15thNight
36%46%14%22%16%
2112
16th to endNight
36%5%6%16%19%16%
1893
March1st to 15thNight
30%5%9%21%21%11%
2024
16th to endNight
31%410%18%22%12%
2112
April1st to 15thNight
31%5%8%18%23%12%
1976
16th to endNight
25%6%11%24%21%10%
1717
May1st to 15thNight
26%9%13%19%19%11%
1620
16th to endNight
30%10%14%22%17%5%
1684
June1st to 15thNight
36%11%20%20%9%1
1620
16th to endNight
38%12%17%19%9%2
1620
July1st to 15thNight
36%14%23%18%5%
1530
16th to endNight
38%11%26%19%4
1595
August1st to 15thNight
39%15%25%15%3
1671
16th to endNight
43%15%17%16%5%1
1943
September1st to 15thNight
44%11%15%14%12%2
1980
16th to endNight
41%9%13%15%13%6%
1903
October1st to 15thNight
29%5%8%21%20%14%
1823
16th to endNight
29%46%14%27%18%
2112
November1st to 15thNight
29%47%19%23%16%
2167
16th to endNight
30%48%16%22%17%
2340
December1st to 15thNight
36%6%10%18%20%7%
2340
16th to endNight
42%5%7%20%14%9%
2496

Seeing (when cloud cover <= 80%)
Color Meanings:
Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
15%11%36%17%8%10%
90
16th to endDay
16%18%33%20%9%1
96
February1st to 15thDay
11%16%31%28%12%
90
16th to endDay
8%9%30%40%8%1
81
March1st to 15thDay
12%432%33%16%
225
16th to endDay
10%425%32%23%3
288
April1st to 15thDay
12%10%19%29%24%4
270
16th to endDay
7%418%28%28%12%
270
May1st to 15thDay
9%415%30%26%13%
288
16th to endDay
8%16%22%30%31%
331
June1st to 15thDay
9%16%14%30%37%
315
16th to endDay
11%213%27%44%
315
July1st to 15thDay
7%37%29%52%
305
16th to endDay
5%38%30%50%
326
August1st to 15thDay
12%1412%32%36%
313
16th to endDay
10%6%13%25%43%
332
September1st to 15thDay
16%8%16%30%26%
315
16th to endDay
17%8%21%33%18%
283
October1st to 15thDay
14%113%31%30%8%
255
16th to endDay
8%222%29%28%8%
272
November1st to 15thDay
12%320%34%21%7%
196
16th to endDay
5%431%37%12%8%
90
December1st to 15thDay
11%11%26%30%12%8%
90
16th to endDay
27%7%14%35%11%4
96
January1st to 15thNight
14%9%32%33%9%1
720
16th to endNight
16%9%31%32%9%
768
February1st to 15thNight
14%9%29%36%10%
704
16th to endNight
14%6%35%37%5%
631
March1st to 15thNight
11%6%30%39%11%
720
16th to endNight
10%6%28%34%19%
768
April1st to 15thNight
11%5%25%39%16%1
718
16th to endNight
6%228%38%23%1
544
May1st to 15thNight
10%120%37%27%3
540
16th to endNight
6%113%32%40%5%
563
June1st to 15thNight
8%433%43%9%
540
16th to endNight
7%327%46%14%
540
July1st to 15thNight
8%323%46%17%
510
16th to endNight
5%1318%53%17%
564
August1st to 15thNight
8%319%53%14%
539
16th to endNight
11%422%42%17%
606
September1st to 15thNight
11%17%24%43%11%
720
16th to endNight
12%113%31%36%3
689
October1st to 15thNight
11%116%35%31%3
660
16th to endNight
9%421%34%27%1
704
November1st to 15thNight
11%421%39%22%2
700
16th to endNight
11%6%29%33%18%
720
December1st to 15thNight
14%5%28%33%16%1
720
16th to endNight
16%6%28%31%16%
768
Page generated at 2017-09-24 09:15:57. Version ac04

Copyright 2017 A. Danko


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